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Fast Spatial Intersection and Union Using GDAL

Source: R/util_nps_union.R
util_nps_union.Rd

Performs a spatial intersection and union of two sf objects using GDAL's optimized spatial operations. This function is significantly faster than native sf operations for large datasets.

Usage

util_nps_union(
  sf1,
  sf2,
  gdal_path = NULL,
  chunk_size = NULL,
  cast = FALSE,
  verbose = TRUE
)

Arguments

sf1

An sf object containing polygons. All non-geometry columns will be preserved in the output

sf2

An sf object containing polygons. All non-geometry columns will be preserved in the output

gdal_path

Character string specifying the path to GDAL binaries (e.g., "C:/OSGeo4W/bin"). If NULL (default), assumes GDAL is in system PATH

chunk_size

Integer. For large datasets, process in chunks of this many features from sf1. Set to NULL (default) to process all at once

cast

Logical. If TRUE, will cast multipolygon geometries to polygons before processing. Default is FALSE, which keeps multipolygons as is (usually faster).

verbose

Logical. If TRUE, will print progress messages. Default is TRUE.

Value

An sf object containing the spatial intersection of sf1 and sf2, with geometries unioned by unique combinations of all attributes from both input objects

This function uses GDAL's ogr2ogr utility to perform spatial intersection operations, which can be much faster than sf's native functions for large datasets. The process:

  1. Exports both sf objects to temporary GeoPackage files

  2. Combines them into a single file

  3. Dynamically builds SQL query based on actual column names

  4. Uses SQL with spatial functions to find intersections

  5. Groups and unions results by all attribute combinations

For very large datasets that cause memory issues, the function can process data in chunks.

The function automatically detects all non-geometry columns from both input objects and includes them in the intersection operation.

Note

Requires GDAL/OGR to be installed and accessible. On Windows, this is typically provided by OSGeo4W or QGIS installations, downloadable at https://trac.osgeo.org/osgeo4w/.

Examples

if (FALSE) { # \dontrun{
data(tbsubshed)
data(tbjuris)
result <- util_nps_union(
  sf1 = tbsubshed,
  sf2 = tbjuris,
  "C:/OSGeo4W/bin"
  )
} # }